1. Field of the Invention
This invention relates to knitting parts such as a guide, needle, tongue, sinker, separator, jacquard guide needle and the like which have a portion contacting with knitting yarn when the parts are fitted to a knitting machine to perform knitting, and particularly to surface covering technology to improve the durability of such parts.
2. Description of the Related Art
The present invention will be described using a warp knitting machine as an example, though knitting machines may include a warp-, flat- and circular knitting machine and the like, and similarly it can be applied to such a flat- or circular machine.
The warp knitting machine is roughly classified into tricot and raschel machines, on which a sectional beam wound with knitting yarn or warp end is usually mounted, the warp end being supplied therefrom to a knitting needle line to perform knitting.
The knitting parts (tool) consisting of a knitting section of a warp knitting machine comprise a thin sheet formed "guide" of about 200 .mu.m thick which is located between a sectional beam and a knitting needle line and has a hole to guide knitting yarn or warp end, a thin sheet-formed "needle" with a hook on a head end for knitted stitch formation, and a thin sheet-formed "tongue", which cooperatively participates in the knitted stitch formation together with the needle, and "sinker", as well as "separator", "jacquard guide needle", etc., in general, a number of such parts being arranged parallel at very close spaces to form a block.
Generally, from viewpoints of easy processing and wear resistance, a carbon steel base material shaped to profile each of these parts is coated by means of wet chromium plating and used as various knitting parts described above.
The durability of such knitting parts, however, has been in serious question due to speeding up of knitting machines, diversification of materials for knitting yarn such as high strength fibers or modified fibers and employment of various kinds of sizes.
Namely, the knitting parts such as the guide, needle, tongue, sinker, separator, jacquard guide needle, etc. tend to be worn out at the portion contacting with the knitting yarn, which would cause hairiness or end breakage of the yarn, and thus the durability of such parts is an important factor in deciding the operational effectiveness of machines and the cost of products because it requires a great deal of expense, effort and time to replace a great number of these parts used in a machine so as to prevent such a trouble of the yarn described above.
It has been proposed to coat the surface of knitting parts (tool) for warp knitting machines with high hardness covering of metals such as tantalum (Ta), tungsten (W), titanium nitride(TiN), titanium-tungsten alloy (TiW), etc. (see Japanese Laid-Open Patent No. 4-41,755).
It has also been known, however, that wearing of knitting parts typically represented by the needle or guide is a phenomenon caused by kinds of fibers, impact pressure, vibration characteristics, etc., and that satisfied results are not necessarily obtained by a covering of high surface hardness.
In fact, in the case of a needle or guide covered with titanium nitride which is known as a covering of a high hardness compound, no increase in durability was observed, compared with a conventional one covered by means of chromium plating on a surface of carbon steel base material, and caused a problem in that the substrate was softened due to a higher treating temperature.
Further, it is also reported that the toughness of a base material itself is lost and, as a result, durability is decreased on the contrary when a covering of high hardness is thickly formed on the base material. From this point of view, it is necessary to improve the durability without spoiling inherent properties of the base material.
Upon this, the inventors have confirmed it effective to form a hard carbon film covering on a surface of base material of knitting parts of knitting machine such as a needle, guide and the like thereby markedly improving durability compared with conventional parts covered only by chromium plating.
However, it is very ineffective to cover the surface of each knitting part with the hard carbon film by means of a vapor phase film forming method such as plasma CVD (Chemical Vapor Deposition) method, because a broader plasma space is required for each part.
Accordingly, it is assumed that, if any measure as to abrasion resistance is taken only on a portion of each knitting part contacting with knitting yarn, durability is sufficiently improved and a bulk handling thereof in a lump becomes feasible during a vapor phase film forming step, which should be considerably productive.
In order to partially cover the surface of parts by the vapor phase film forming method, in general a metal mask is mechanically contacted with the surface of parts or a resist is formed on a portion where the covering is not to be applied so as to cover as a whole, followed by a lift-off of the mask or the resist thus applied, which would result in a steep difference on the surface of parts between a covered and uncovered layer portions.
While the knitting yarn is knitted at high speed with dancing, the yarn does not always contact with a constant portion on the surface of parts but comes into contact irregularly over a wide range of the surface of parts where durability is required. Consequently, such a problem would happen, even in a portion where durability is not so much required, that the knitting yarn is caught in the steep difference in layer due to covered and uncovered portions to cause a hairiness or end breakage thereof.
Accordingly, present invention has been developed in view of the technical background described above, and it is an object of this invention to provide knitting parts of a knitting machine having markedly improved durability and excellent productivity without causing any hairiness nor end breakage.